Steve Trevelyan
Generally a builder or a specialist in this field .Really depends on the problem , a builder can tank walls with a plastic barrier in bad cases , dpc injection into walls , liquid membranes painted on walls , or source of damp rectified , i.e., leaking gutters, leaking drains , dpc bridged , lack of ventilation ....so many variables and to be honest can be sorted by a wide range of tradesmen.
